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Okay, my wife had to buy a new key for her 2001 E46 for $225.00 because the remote in the original key would not charge up no matter what. After searching for all of the forums, I have found there is no real concrete answer about replacing the battery in a remote. Since I had an old one, I figured "what the hell" and I would give it a go. Here is what I found out...
You CAN replace a battery, but you must have a little patience and some special tools.
Here is what you need:
1) Small jewelers screwdriver (flathead)
2) Razor blade
3) Soldering gun
4) JB weld ($5.00)
5) New battery (Panasonic VL-2020 Lithium Coin Cell battery: $5.00)
6) Super glue ($2.00)

I could not find any place in Seattle to buy that battery, so I found a place online called Mouser Electronics (www.mouser.com), and got one for $5.00 and $5.00 shipping, so ten bucks for the battery.

Replacement Procedures:

1) Gently pry open the key by forcing the screwdriver in the rear center of the key. You will score the plastic, but the battery sits back there and you are away from the electronics for the remote. My key split open fairly easily, but the edges were rough, so I smoothed them down with the razor blade.
2) Pop out the board inside of the key, you can't miss the battery. You can see the battery has a positive and negative lead soldered to the board. Using your soldering gun, melt off the solder that is holding the leads to the board. The battery will fall off.
3) The leads on the battery I got were similar, but did not line up exactly, so I had to bend one of the leads to fit the hole pattern on the board. You can also pry off the leads on the old battery if you want, they are tacked on, but you can pop them off with the screwdriver. My soldering skills are lacking, so I used a little dab of JB weld to hold the new leads in place.
4) Put the board with the new key back into the key housing. Put a little super glue on the edges of the housing and press the two parts of the housing together until they are secured (Make sure the board and battery are installed correctly!)
5) You have to initialize the key. (This is covered a lot in the forums.) You must do both keys at the same time. I re-initialized the new key, then the old one I had just put the battery in. Both checked out, viola! Extra key now works!

So, 15 minutes later and about $20.00, I have an extra key that is fully functional. If you want to save $200 bucks and have a little time, you can make an old key remote work again, or just use your key manually. Hope this helps someone!

Just a follow up, after reading my post just wanted to clarify that when you are reinserting the battery into the board, it is still best to use the solder to connect the leads to the board, I just used the Jb weld to make sure it was secured as JB weld doesn't conduct electricity, so just remelt the solder that is still on the board to attach the leads. No biggie, just wanted to clarify...sorry.

Thank you benmuellerb! I'll be doing this tonight as long as I can find this battery! I've been going ghetto style with manually locking and unlocking the car for the past couple weeks since the dealer said it was $200+ for the new key.

4) Put the board with the new battery back into the key housing. Put a little super glue on the edges of the housing and press the two parts of the housing together until they are secured (Make sure the board and battery are installed correctly!)

no prob... i just wanted to make sure other readers didn't get thrown for a loop. on a side note, i made sure i drove with my other key to make sure i wouldn't need to invoke this cool process. hahaha. good job OP.

Quote:

Originally Posted by benmuellerb

To Hammer 88, yes, you are correct. mine directions were a little off there. sorry about that.

You are correct, i replace my battery i bought it at interstate battery, its a panasonic VL2020 rechargeable, the battery is spot welded to the connector
not soldered when you remove the connector from the battery you wont be able to spot weld it back it requires a spot welding machine very expensive
here is the alternative like the first thread said desolder the old connector with the battery, remove the old battery then solder the new connector with battery to the board, easy fix

it's a lithium, rechargable. I ordered the horizontal version. Paid for hsipping, then checked the map and figured out that the place is only about 30 minutes from where I work....oh well. Better than driving all that way for a $5 battery.

A couple notes:
------------
1) My key did NOT split apart easily. Maybe the glue was old or something, but I had to work at it for like 10 minutes with a knife and a flathead to get it open. Now, the edges are really rough and the key has visible signs of being opened, but its OK because it actually works now.

2) I did purchase the horizontal version of the battery. As mentioned in prior posts, the leads did not match up to the holes on the circuit board. Unlike other posts, however, I was not able to easily bend them such that they would fit, so I had to use a piece of wire to get the lead the rest of the way to the solder pad. As a precaution, people who are unfamiliar with soldering should get help from a friend who has experience.

Other than that, the process worked great. My key can now consistently open the doors from over 20 yards away - a big improvement over the intermittent close-range behavior I had been dealing with. Thanks benmuellerb.